This project deals with both the laboratory and clinical aspects of infection caused by the intestinal nematode, Strongyloides stercoralis. The laboratory research involves analysis and characterization of parasite antigens. The clinical studies focus upon the immune response of infected individuals, and factors that influence the immune response. Experimental infections with the parasite in a newly recognized animal host, the jird (Meriones unguiculatus), have been initiated recently. The recombinant gene product from a cDNA library from 3rd stage parasite larvae was transferred to a pMAL vector. The recombinant product from the new vector is reactive by Western blot with sera from S. stercoralis-infected patients. It shows a high degree of sequence homology with collagen genes of C. elegans. Collaborative clinical studies on patients infected with S. stercoralis were initiated in Bahia, Brazil. The immune response in patients also infected with the retrovirus, HTLV-1, is of particular interest. Serum samples as late as 1 1/2 years after Ivermectin or thiabendazole treatment of strongyloidiasis in Cambodian refugees were found to show a mixed pattern of response. Several human strains of S. stercoralis were found to have a very low efficiency of infection for the jird (Meriones unguiculatus) in comparison to a parasite strain from the dog. Infection with the dog strain was enhanced by administration of prednisolone.